Our aim is to define the basis and pathogenetic mechanism of cell injury caused by actinomycin D (AM) and the related DNA-binding carcinocidal agents dauno-, nogalo- and mithramycin, and aflatoxin Bl. We propose to seek an explanation for the vulnerability of certain proliferating cell types in vitro (e.g. HeLa, HEp2) to acute lethal damage, and the relative resistance of others (e.g. Vero) to the effects of these agents when drug is equally bound and effective in suppressing transcription. We will describe the kinds of premitotic and reproductive pathology caused by AM (and related agents), the manifestations of which appear after drug has been eliminated. These experiments will involve determination of those species of RNA critical for viability, and their role; study of alterations in structure and composition of chromatin, and their genesis; the preagonal events in the cytoplasm; and the rescue of otherwise fatally poisoned cells by hybridization. Resistance to injury and the factors involved in effecting recovery of cells from poisoning will be explored by: determining the order of resumption of synthesis of the RNAs; the role of cytoplasmic factors that initiate nuclear reactivation, and nuclear proteins. The lag in restarting DNA synthesis and division in Vero cells recovering from AM will be explored in terms of damage to DNA and its repair; and the availability of proteins of cytoplasmic origin that stimulate DNA synthesis. Subsequent postmitotic (reproductive) injury including chromosomal and other radiomimetic aberrations will be examined. The conditions in which AM and related agents convert cells in culture toward carcinogenic transformation will be sought.